Photoredox-Catalyzed Plastic Waste Conversion: Nonselective Degradation versus Selective Synthesis

Abstract

Plastic waste pollution is becoming one of the most pressing environmental crises due to the large-scale production without satisfactory recycling schemes, especially with the outbreak of the COVID-19 pandemic in recent years. Upcycling of plastic waste into valuable chemicals powered by solar energy presents a substantially untapped opportunity to turn waste into treasure. In this review, the fundamental principles from plastic nonselective degradation to selective synthesis are first clarified. Then, we aim to outline the representative recent advances in photoredox-based catalytic plastic waste conversion. Particular emphasis is placed on the valorization of plastic waste regarding nonselective degradation versus selective synthesis. Finally, we present challenges and individual insights for further exploration of the plastic waste conversion domain. It is anticipated that this timely and critical review would provide an instructive direction and foresight on the selective conversion of plastics to valueadded chemical feedstocks, thus stimulating the development of a circular and sustainable plastic economy in the coming decades.

Optimization of p-Type Cu2O Nanocube Photocatalysts Based on Electronic Effects

“…Moreover, the CO generation rate on C-30 is 4.91 μmol·g –1 ·h –1 , which is higher than that on existing single-component Cu 2 O nanostructures and even better than that of some Cu 2 O-based hybrid photocatalysts (Table S4). In principle, the hybrid photocatalysts with a Z-scheme heterojunction should have better photocatalytic performance , because the interfacial Schottky barrier can facilitate the photoexcited electron–hole pair separation and enhance the efficiency of charge carrier injection to adsorbate molecules . However, this is not the case shown in this work.…”

Systemically Understanding Aqueous Photocatalytic Upgrading of Microplastic to Fuels

“…[ 22 ] Additionally, other polymers such as expanded polystyrene, polyethylene vinyl acetate, ethylene propylene diene monomer rubber, poly(oxymethylene), polyacrylonitrile, and poly(deca‐4,6‐diynedioic acid) (PDDA) have been detected in water systems. The classification of MPs into two main classes based on polymer structures is significant for understanding plastics’ chemical nature, as MacLeod et al [ 23 ] and Xu et al [ 24 ] proposed. Homogenous chain (homo‐chain) plastics refer to those with C–C backbones, while heterogenous chain (hetero‐chain) plastics have heteroatoms as the bridge in their polymer structure.…”

“…[ 37 ] In the photocatalytic process, these semiconductors possess high‐energy holes (at low VBs) to oxidize surface adsorbed species (water, OH − , or others) to free radicals such as ·OH (2.38 V vs NHE, pH = 0, Figure 3b) and high‐energy electrons (at high CBs) both to reduce protons or water to H 2 (0 V) and to turn O 2 to the ·O 2 − radical (−0.046 V). Then both radicals from the VBs and CBs are involved in the reactions with MPs, which can have a double‐edged sword effect reported by Zhang et al [ 24 ] As a result, MPs react with the free radicals and leach into the water, producing smaller particles with oxygenated fuel‐like molecules and even CO 2 . Though the H 2 in the photoforming process is directly reduced from water, the oxidation of C–H or C–OH would generate H 2 O in the aqueous system again.…”

Revolutionizing fuel production through biologically synthesized zero-dimensional nanoparticles

“…CQDs have found wide-ranging applications in photocatalysis, 23 bio-imaging, 24,25 optoelectronics, 26 drug delivery, 27 photocatalytic organic transformations 28 and sensors. 29 Zhang et al 30 explored plastic conversion using a photoredox-based catalytic system and highlighted the transformation in terms of selective synthesis and nonselective breakdown. Qi et al 31 discussed the progress of supportive photoredox coupling of hydrogen generation with a variety of selective organic transformations such as alcohol oxidation, oxidative cross-coupling, methane conversion, etc.…”